Male pattern baldness is the common type of hair loss that develops in most men at some stage. The condition is sometimes called androgenetic alopecia. It usually takes 15-25 years to go bald. However, some men go bald in fewer than five years.
Male pattern hair loss is an inherited condition, caused by a genetically determined sensitivity to the effects of dihydrotestosterone, or DHT in some areas of the scalp. DHT is believed to shorten the growth, or anagen, phase of the hair cycle, from a usual duration of 3-6 years to just weeks or months. This causes miniaturisation of the follicles, and producing progressively fewer and finer anagen hairs. The production of DHT is regulated by an enzyme called 5-alpha reductase. Several genes are involved, accounting for differing age of onset, progression, pattern and severity of hair loss in family members. The susceptibility genes are inherited from both mother and father.